audio policy: fix USB mic selection for VoIP

When transitioning from speaker phone to normal mode and a USB
headset is connected, we must force a teardown of active input
as the new input device cannot be reached via current input stream.

Bug: 24406915.
Change-Id: I9f7c1d3f3cba285c25a6da1d54a3d15a5c1f378a
1 file changed